RTT CAS無鎖機制

程序對數據操作流程:

        讀數據   改寫   回寫

   

解決數據一致性問題

 

1. 主存和獨立工作區的數據一致性

volatile SIndexes _indxes; 主存中線程可見數據(不做緩存機制直接操作主存儲器)

CachePtrType advance_w()             {                 SIndexes oldval, newval;                 do                 {                     oldval._value = _indxes._value; /*Points to a free writable pointer.*/                     newval._value = oldval._value; /*Points to the next writable pointer.*/                     // check for full :                  if ((newval._index[0] == newval._index[1] - 1) || (newval._index[0] == newval._index[1] + _size - 1))                     {                         return 0;                     }                     newval._index[0]++;                     if (newval._index[0] >= _size)                         newval._index[0] = 0;                     // if ptr is unchanged, replace it with newval.                 } while (!os::CAS(&_indxes._value, oldval._value, newval._value));                 // frome here on :                 // oldval is 'unique', other preempting threads                 // will have a different value for oldval, as                 // _wptr advances. As long as oldval has not been written,                 // rptr will not advance and wptr will remain stuck behind it.                 // return the old position to write to :                 return &_buf[oldval._index[0]];             }

 

CAS(&_indxes._value, oldval._value, newval._value) 爲false:

程序在行過程中，數據區已經讓人串改過，結果已經不可信，那麼繼續執行程序並判。